Abstract
AbstractThe steady‐flow behavior of five samples of branched poly(vinyl acetate) has been studied with the Weissenberg rheogoniometer. The branching densities and molecular weight distributions were known from an analysis of the polymerization kinetics. Measurements were made on concentrated diethyl phthalate solutions (0.170 and 0.225 g/ml) at temperatures of 30 and 70°C. The viscosities of all solutions at zero shear rate were less than of solutions of linear poly(vinyl acetate) with the same weight‐average molecular weight. The amount of decrease was in excellent agreement with Bueche's theory of melt viscosity in branched systems. The viscosity versus shear rate curves were surprisingly independent of molecular weight distribution, the data from all samples being superimposable on the same master curve. Relaxation times derived independently from the viscosity behavior and the normal stress data were of similar magnitude and always close to the Rouse relaxation time of each solution.
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